Please explain with examples (i.e. numbers) as I am having a bit of trouble answering.

Question

A public school system wanted to know whether the reading levels of the students at two of its schools were different. The study that was conducted tested an enormous number of students, and concluded that students attending School A scored significantly higher than those attending School B. However, the difference between the means of the two schools was very small. What should a person conclude regarding the difference in reading levels between the two schools? Explain what the conclusion would be to a person who is familiar with the basic logic of hypothesis testing, but knows nothing about power.